In many industrial, military, security or medical applications, images of the internal structure of objects is required. Radiography is often used for imaging. Radiography generally comprises either conventional transmission radiography or backscatter radiography.
FIG. 1 is a schematic illustrating the configuration used for conventional transmission radiography. In conventional radiography, an image is formed by transmitting radiation from a radiation generator 105 through an internal detail 110 within object 130. Attenuated radiation is received by a radiation detector 115 which is disposed on the side of the object opposite to that of the radiation generator 105. In the case of tomography, the object 130 is generally rotated about axis perpendicular to the plane of the figure.
FIG. 2 is a schematic illustrating the configuration used for backscatter radiography. Unlike conventional radiography which relies on transmission, in backscatter radiography radiation is scattered by internal detail 210 within object 230. In backscatter radiography, the radiation generator 205 and radiation detector 215 are on the same side of the object 230. All backscatter radiography techniques allow one-sided imaging of the object since the radiation generator 205 and the radiation detector 215 are located on the same side of the object 230. This is the same imaging configuration that people and animals use for optical viewing of the surroundings. Because of the absence of a refraction process for the penetrating radiation in backscatter radiography, image-gathering lenses cannot be used.
In backscatter radiography, illumination of an entire region of the object to be interrogated in a single snapshot has generally only been possible using a pinhole, coded aperture, or a restriction positioned between the object and the radiation detector. This generally results in either extremely inefficient sensing of the radiation, or the introduction of substantial image-obscuring structured noise, thus requiring large exposure times for typical radiation sources. An alternative includes use of a scanning pencil or fan beam for illuminating a temporal sequence of points or lines on the object surface. This also yields long exposure times and decoding algorithms having long calculation times, besides requiring an expensive scanning apparatus.
The equivalent of an optical snapshot camera capable of implementation using relatively inexpensive components which would provide high image resolution and a short exposure time would be desirable for applications which require one-sided imaging of the internal structure of objects.